A breakthrough by researchers could mean that testicle tissue from boys facing cancer treatment could be saved - by transplanting it into mice.

Experts managed not only to successfully transplant tissue from a goat and a pig under the skin of the mouse, but then watched it mature until fully-formed sperm could be harvested from it.

It is the first time such a cross-species transplant has been so successful.

Many types of chemotherapy destroy the cells in the testicle which make sperm, making the patient infertile.

After puberty, males can freeze a sample of sperm which can be thawed later.

It is possible that adults will soon be able to freeze small sections of tissue which could be reimplanted later to restore full fertility.

However, little can be done at present to help pre-pubescent children, as they cannot produce sperm or mature testicular tissue to freeze.

Under the skin

Dr Ina Dobrinski from the school of veterinary medicine at the University of Pennsylvania managed to graft fragments of newborn pig and goat testes under the skin of mice.

These had been given immunosuppressant drugs to reduce the chance they would "reject" the foreign tissue.

Once in place in the adult mice, the immature tissue grew and developed into small "testes" under the skin.

These matured and began to produce fully-functioning sperm, relying on the natural hormones of the mouse to make this happen.

More than 60% of the grafts survived and produced working sperm, they reported to the journal Nature.

We are constantly researching types of chemotherapy that are less damaging

Spokesman, Leukaemia Research Fund

While the lifespan of the mouse host is limited - and would not stretch the 10 years or more needed if tissue was transferred from a pre-pubescent human, the advance proves in principle what could be achieved.

The researchers suggested it could produce a limitless supply of sperm for a would-be father, rather than the limited amount that could be stored prior to chemotherapy.

They said it could also be used to "piggy-back" the sperm of endangered species, or rare breeding animals.

No need

However, a spokesman for the Leukaemia Research Fund said that advances in treatment would hopefully mean that such techniques would never have to employed in humans.

He said: "We are constantly researching types of chemotherapy that are less damaging, and trying to identify patients on whom we can use less severe treatments.

"Things are improving all the time. We often hear of cases of women who were told they would never be able to have children who have just managed it."